This invention relates to a low cost austenitic stainless steel having relatively low nickel and manganese levels with properties equal to or better than AISI Types 301 and 304. The steel of this invention exhibits good hot working properties, good weldability and can be fabricated into a variety of products from both the hot worked and cold worked conditions such as strip, tubing, bar and rod. It has particular utility in the production of cold headed fasteners from cold drawn wire.
The steel of the present invention possesses the further advantage of being precipitation hardenable in the cold worked condition, particularly when drastically cold reduced 60%, in which condition it exhibits a 0.2% offset yield strength of 165 to 182 ksi, an elongation in 5 cm of at least 10% and a Rockwell C hardness of 45-50.
AISI Type 301 has a nominal composition of 0.15% maximum carbon, 2.00% maximum manganese, 0.045% maximum phosphorus, 0.030% maximum sulfur, 1.00% maximum silicon, 16% to 18% chromium, 6% to 8% nickel and balance iron.
AISI Type 304 has a nominal composition of 0.08% maximum carbon, 2.00% maximum manganese, 0.045% maximum phosphorus, 0.030% maximum sulfur, 1.00% maximum silicon, 18% to 20% chromium, 8% to 12% nickel, and balance iron.
In contrast to this, the austentitic stainless steel of the present invention contains from about 1.5% to 3.0% manganese, 3% to 4.7% nickel, 1.75% to 3% copper, 0.10% to 0.30% nitrogen and up to about 0.3% columbium, titanium, tantalum, or mixtures thereof.
U.S. Pat. No. 3,357,868 to Tanczyn discloses a precipitation-hardenable stainless steel containing 0.05% maximum carbon, 15% maximum manganese, 2% maximum silicon, 10% to 25% chromium, 4% to 15% nickel, 0.25% maximum nitrogen, 1% to 5% copper, 0.3% to 4% columbium, 5% maximum molybdenum, and balance essentially iron.
U.S. Pat. No. 3,615,366 to Allen discloses a precipitation-hardenable stainless steel containing 0.15% maximum carbon, 3% to 10% manganese, 1% maximum silicon, 15% to 19% chromium, 3.5% to 6% nickel, 0.04% to 0.4% nitrogen, 0.5% to 4% copper, and balance essentially iron.
U.S. Pat. No. 3,284,250 to Yeo discloses a steel containing 0.03% to 0.12% carbon, 10% maximum manganese, 2% maximum silicon, 16% to 20% chromium, 3% to 12% nickel, 0.5% maximum nitrogen, 0.15% to 0.3% columbium, 3% maximum molybdenum, 0.5% maximum aluminum, and balance essentially iron. When hot rolled within the temperature range of above 1900.degree. to about 2300.degree. F. and cold rolled without the usual process anneal between hot rolling and cold rolling the resulting cold rolled product is alleged to exhibit a yield strength of at least 50 ksi in the annealed condition, an elongation of at least 50% and a very fine grain size.
British Pat. No. 995,068 discloses an austenitic stainless steel consisting of a trace to 0.12% carbon, 5% to 8.5% manganese, 2.0% maximum silicon, 15.0% to 17.5% chromium, 3.0% to 6.5% nickel, 0.75% to 2.5% copper, a trace to 0.10% nitrogen, and remainder iron, with the constituents being controlled so that the martensite-forming characteristic is less than 10% according to a formula and the delta-ferrite forming characteristic is less than 10% according to a formula. Copper is also controlled so that it does not exceed 3.85%-0.18%.times.% manganese. The steel is stated to have high austenite stability and a low work hardening rate, due to avoidance of transformation to martensite during cold working.
Other U.S. patents disclosing austenitic stainless steels containing copper and nitrogen include No. 3,071,460 to Tanczyn, No. 3,282,684 to Allen, No. 3,567,528 to Mohling, No. 2,797,993 to Tanczyn, No. 2,784,083 to Linnert and No. 4,022,586 to Espy.
Other background prior art of which applicants are aware includes U.S. Pat. Nos. 2,797,992; 2,871,118; 3,615,368; 2,784,125; 2,553,706; 3,753,693; 3,910,788; and 2,527,287.
Despite the great variety of austenitic stainless steels now known, including precipitation-hardenable stainless steels, applicants are not aware of an austenitic prior art steel containing less than 5% nickel which exhibits the combination of high strength and hardness and good ductility when drastically cold reduced, together with good corrosion resistance, good hot workability and avoidance of weld area cracking in fusion weldments.
It is a principal object of the present invention to provide an austenitic stainless steel having the above novel combination of properties.
It is a further object of the invention to provide an austenitic stainless steel of low cost having properties substantially equivalent to those of AISI Types 301 and 304.
According to the invention, there is provided an austentic stainless steel having good hot workability, a 0.2 offset yield strength of 165 to 182 ksi and an elongation in 5 cm of at least 10% if cold reduced 60%, the steel consisting essentially of, in weight percent, 0.05% maximum carbon, about 1.5% to about 3.0% manganese, about 0.06% maximum phosphorus, about 0.035% maximum sulfur, about 1% maximum silicon, about 15% to about 20% chromium, 3% to 4.7% nickel, about 1.75% to 3% copper, about 0.10% to about 0.30% nitrogen, up to about 0.3% columbium, titanium, tantalum, or mixtures thereof, and remainder essentially iron.